1. Field of the Invention
The present invention relates to an electrophotographic color image forming apparatus, and more particularly, to an electrophotographic color image forming apparatus including a plurality of photosensitive media, a belt contacting the photosensitive media, and a plurality of transfer rollers facing the photosensitive media as interposing the belt between them.
2. Description of the Related Art
An electrophotographic color image forming apparatus is an apparatus for printing an image by: scanning light onto a photosensitive medium that is charged to a predetermined potential to form an electrostatic latent image on an outer circumferential surface of the photosensitive medium; developing the electrostatic latent image by injecting a toner, that is, a developing agent, into a visible image of a predetermined color; and transferring the visible images of different colors onto paper and fusing the images on the paper. FIG. 1 shows a conventional electrophotographic color image forming apparatus.
Referring to FIG. 1, the conventional electrophotographic color image forming apparatus includes: a first photosensitive medium 10 and a second photosensitive medium 11; a first scanner 12 and a second scanner 13 scanning light onto the pair of photosensitive media 10 and 11; and four developers 15, 16, 17, and 18 receiving toners of four colors, that is, yellow (Y), cyan (C), magenta (M), and black (K) colors to form the color image by overlapping colors. The Y and C developers 15 and 16 face the first photosensitive medium 10, and the M and K developers 17 and 18 face the second photosensitive medium 11.
In addition, an intermediate transfer belt 20, on which the visible images formed on the photosensitive media 10 and 11 are transferred, is supported by a driving roller 21 and an idle roller 22 to be circulated, and proceeds while contacting lower portions of the pair of photosensitive media 10 and 11. A first transfer roller 25 and a second transfer roller 26 are formed so that transfer nips can be formed on respective contacting areas of the intermediate transfer belt 20 and the first and second photosensitive media 10 and 11. The first and second transfer rollers 25 and 26 respectively face the first and second photosensitive media 10 and 11 while interposing the intermediate transfer belt 20 between the rollers and the photosensitive media.
The color image formed on the intermediate transfer roller 20 by the overlapped transfer operations is transferred onto a sheet of paper (P) passing through the transfer nip between the intermediate transfer belt 20 and a third transfer roller 30. A transfer backup roller 23 is positioned adjacent to the third transfer roller 30 with the intermediate transfer belt 20 interposed therebetween, so that a transfer nip can be formed between the intermediate transfer belt 20 and the third transfer roller 30.
In the above conventional electrophotographic color image forming apparatus, a pair of photosensitive media 10 and 11 and a pair of transfer rollers 25 and 26 are pressed with each other. In addition, soft rollers having outer circumferential surfaces formed of elastic material such as rubber are used as the transfer rollers 25 and 26 to increase the width of the transfer nip.
Accordingly, pressure between the photosensitive media 10 and 11 and the intermediate transfer belt 20 increases, and irregular impact between the photosensitive media 10 and 11 and the intermediate transfer belt 20 increases, which causes a transfer defect and an image jitter. In addition, since the soft roller is used as the transfer roller, the fabrication costs increase, and it is difficult to maintain size accuracy of elements.